You don't need the registration email because your account is more than 6 months old, so this rule is optional.

10. You must provide a screenshot of the verification e-mail you got from Nexon after registering your account and the e-mail must be in your inbox. You must also provide the buyer with the original e-mail at the time or purchase. Resold accounts will no longer be permitted to be sold. (For Members who are older than at least 6 months, following this rule is optional)